There is known a data supply device which receives input of image data from a video supply device, and then wirelessly transmits the image data thus input to a display device such as a projector. In such a data supply device, there is known a technology of beam forming for controlling the direction of an electrical wave (beam) to a specific direction (e.g., PTL1). In PTL1, there is described a technology of dynamically switching the direction of the beam in order to search for an optimum transmission channel.